The present invention relates to an apparatus used in conjunction with a wastewater treatment process involving the recycling of activated sludge into raw or partially treated wastewater to catalyze the degradation of organic compounds by aerobic microorganisms. More particularly, the present invention relates to an apparatus which optimizes the amount of oxygen available to microorganisms, allowing them to more effectively metabolize organic waste compounds.
The recycling of sludge containing "waste eating" bacteria and other organisms (activated sludge) into raw sewage or partially treated wastewater is well known in the art. Generally, wastewater is directed into a shallow confines area, such as a tank or ditch with a large surface area exposed to the air to promote the growth of bacteria and other microorganisms which feed on organic waste. The wastewater is allowed to commingle with the air and means are often provided to increease the air/wastewater interface to enhance the organic decomposition of suspended wastes. Supplemental agitation means are also used to maintain solid waste material in a suspended state as long as possible. Examples of aeration devices include forced air sparger jets located under the surface of the water, and mechanical mixing devices such as paddles, rollers, disks or brushes mounted above the surface of the wastewater and extending into said wastewater to cause agitation.
Secondary sludge aeration devices presently in use contain many disadvantages, among them the excessive consumption of power to run the jet aerators as well as the mechanical devices, and the requirement for relatively large areas of land to provide tanks with sufficient surface area.
U.S. Pat. No. 3,703,462 to Smith discloses an attempt to overcome some of these drawbacks, comprising the method of circulating a sewage liquor/air mixture through a hydraulic vertical flow circuit in a manner designed to prevent the escape of substantial amounts of air from such mixture for a major portion of the flow circuit.
A preferred embodiment of the apparatus disclosed by Smith to effectuate his method comprises a generally rectangular tank of considerable depth having gas impermeable baffle-like members positioned below the normal liquid surface to define a plurality of flow passageways therein. Various aeration mechanisms are positioned in one or more of such passageways to introduce air and flow energy to the wastewater within the apparatus.
The baffle-like members delay the escape of air within the passageways, thus allowing increased utilization of oxygen by the aerobic organisms. This more efficient use of oxygen significantly reduces the cost of this activated sludge phase of the waster treatment process. However, a major drawback of the device disclosed by the Smith patent is that air is released from beneath the baffle in a narrow band of bubbles which rapidly migrates to the surface. The emission of entrapped air in this narrow band of bubbles means that the air is not retained for a sufficient duration to maximize the utilization of available oxygen by the wastewater biota. A further drawback of the Smith device is that the air is released in a zone where the hydraulic flow is vertical, and acts to speed the upward migration of released air bubbles.
Thus, it is a major objective of the present invention to provide a secondary wastewater treatment apparatus which allows wastewater biota to make maximum use of available oxygen.
It is a further objective of the present invention to provide an activated sludge wastewater treatment apparatus wherein the retention time of supplemental oxygen is increased over conventional models.
It is a still further objective of the present invention to provide an activated sludge wastewater treatment apparatus wherein the supplemental oxygen is dispersed throughout a wastewater tank in a physical format which maximizes its utilization by treating biota.